There is a case where a drive element is turned on or off according to PWM drive or frequency drive and thereby a load such as, a solenoid, a relay, a heater, or a motor is driven, for control of a vehicle. In the related art, a load drive circuit includes a diagnosis circuit that diagnoses a state of a load which is driven, and diagnoses the state of the load by measuring a predetermined physical quantity of the load drive circuit. There is a case where the diagnosis circuit continuously diagnoses whether or not abnormality occurs in the load which is driven during an operation of the vehicle.
Meanwhile, in a case where the diagnosis circuit fails, a passenger riding in the vehicle may not be aware of the failure, because the diagnosis circuit does not have a function control the vehicle thereby not affecting the operation of the vehicle. In addition, in a case where the diagnosis circuit fails, a vehicle control system is also not able to detect the failure, since there is no function to detect that the diagnosis circuit fails. That is, in a case where a diagnosis circuit fails a potential failure can occur in which a passenger is not able to recognize the failure and the vehicle control system is not able to detect the failure.
If abnormality occurs in a load which is driven in a state where a diagnosis circuit fails, the diagnosis circuit is not able to detect the abnormality of the load, and furthermore, it is also not possible to activate a protection function to protect a load drive circuit from the abnormality of the load. That is, if double failures occur in which abnormality occurs in the load in a state where the diagnosis circuit fails, the protection function is also not able to be activated, and thus, the load drive circuit can be broken in the worst case.
In PTL 1, if a drive stop signal is inputted from a control circuit which controls a drive circuit during initialization processing of a system after an ignition key of a vehicle is turned on or during stop processing of the system after the ignition key of the vehicle is turned off, at least the drive circuit stops, and thereby a normal operation of a diagnosis circuit which diagnoses a state of the load is confirmed in a state where the load drive circuit is incorporated into an electronic control device.